Implantable package to facilitate inspection

ABSTRACT

The present invention is a non-destructive method of inspecting a bond, particularly a braze bond, in a hermetic package. The invention involves a unique hermetic package design adapted for ultrasonic inspection and a method of inspecting the package. This package and non-destructive inspection process are particularly useful in implantable neural stimulators such as visual prostheses.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 13/752,636, filed Jan. 29, 2013, for Method for Inspection ofMaterials for Defects, now U.S. Pat. No. 8,554,328 which is a divisionalapplication of U.S. patent application Ser. No. 13/360,480, filed Jan.27, 2012, for Implantable Package to Facilitate Inspection, now U.S.Pat. No. 8,391,987, which is a divisional application of U.S. Ser. No.12/209,068, filed Sep. 11, 2008, for Method of Inspection of Materialsfor Defects, now U.S. Pat. No. 8,131,376, which claims benefit of U.S.Provisional Patent application Ser. No. 60/971,509, filed on Sep. 11,2007, entitled Method for Inspection of Materials for Defects, thedisclosures of which is incorporated herein by reference.

This application is related to but in no way dependent upon U.S. patentapplication Ser. No. 11/385,314, filed Mar. 20, 2006, for “Package foran implantable Neural Stimulation Device”.

GOVERNMENT RIGHTS NOTICE

This invention was made with government support under grant No.R24EY12893-01, awarded by the National Institutes of Health. Thegovernment has certain rights in the invention.

FIELD OF THE INVENTION

The present invention is generally directed to the design andmanufacture of hermetic packages, and in particular to inspection ofthose hermetic packages to avoid defects. Hermetic packages areparticularly useful of implantable neural stimulators such as a visualprosthesis.

BACKGROUND OF THE INVENTION

In 1755 LeRoy passed the discharge of a Leyden jar through the orbit ofa man who was blind from cataract and the patient saw “flames passingrapidly downwards.” Ever since, there has been a fascination withelectrically elicited visual perception. The general concept ofelectrical stimulation of retinal cells to produce these flashes oflight or phosphenes has been known for quite some time. Based on thesegeneral principles, some early attempts at devising prostheses foraiding the visually impaired have included attaching electrodes to thehead or eyelids of patients. While some of these early attempts met withsome limited success, these early prosthetic devices were large, bulkyand could not produce adequate simulated vision to truly aid thevisually impaired.

In the early 1930's, Foerster investigated the effect of electricallystimulating the exposed occipital pole of one cerebral hemisphere. Hefound that, when a point at the extreme occipital pole was stimulated,the patient perceived a small spot of light directly in front andmotionless (a phosphene). Subsequently, Brindley and Lewin (1968)thoroughly studied electrical stimulation of the human occipital(visual) cortex. By varying the stimulation parameters, theseinvestigators described in detail the location of the phosphenesproduced relative to the specific region of the occipital cortexstimulated. These experiments demonstrated: (1) the consistent shape andposition of phosphenes; (2) that increased stimulation pulse durationmade phosphenes brighter; and (3) that there was no detectableinteraction between neighboring electrodes which were as close as 2.4 mmapart.

As intraocular surgical techniques have advanced, it has become possibleto apply stimulation on small groups and even on individual retinalcells to generate focused phosphenes through devices implanted withinthe eye itself. This has sparked renewed interest in developing methodsand apparatuses to aid the visually impaired. Specifically, great efforthas been expended in the area of intraocular retinal prosthesis devicesin an effort to restore vision in cases where blindness is caused byphotoreceptor degenerative retinal diseases; such as retinitispigmentosa and age related macular degeneration which affect millions ofpeople worldwide.

Neural tissue can be artificially stimulated and activated by prostheticdevices that pass pulses of electrical current through electrodes onsuch a device. The passage of current causes changes in electricalpotentials across visual neuronal membranes, which can initiate visualneuron action potentials, which are the means of information transfer inthe nervous system.

Based on this mechanism, it is possible to input information into thenervous system by coding the sensory information as a sequence ofelectrical pulses which are relayed to the nervous system via theprosthetic device. In this way, it is possible to provide artificialsensations including vision.

One typical application of neural tissue stimulation is in therehabilitation of the blind. Some forms of blindness involve selectiveloss of the light sensitive transducers of the retina. Other retinalneurons remain viable, however, and may be activated in the mannerdescribed above by placement of a prosthetic electrode device on theinner (toward the vitreous) retinal surface (epiretinal). This placementmust be mechanically stable, minimize the distance between the deviceelectrodes and the visual neurons, control the electronic fielddistribution and avoid undue compression of the visual neurons.

In 1986, Bullara (U.S. Pat. No. 4,573,481) patented an electrodeassembly for surgical implantation on a nerve. The matrix was siliconewith embedded iridium electrodes. The assembly fit around a nerve tostimulate it.

Dawson and Radtke stimulated cat's retina by direct electricalstimulation of the retinal ganglion cell layer. These experimentersplaced nine and then fourteen electrodes upon the inner retinal layer(i.e., primarily the ganglion cell layer) of two cats. Their experimentssuggested that electrical stimulation of the retina with 30 to 100 μAcurrent resulted in visual cortical responses. These experiments werecarried out with needle-shaped electrodes that penetrated the surface ofthe retina (see also U.S. Pat. No. 4,628,933 to Michelson).

The Michelson '933 apparatus includes an array of photosensitive deviceson its surface that are connected to a plurality of electrodespositioned on the opposite surface of the device to stimulate theretina. These electrodes are disposed to form an array similar to a “bedof nails” having conductors which impinge directly on the retina tostimulate the retinal cells. U.S. Pat. No. 4,837,049 to Byers describesspike electrodes for neural stimulation. Each spike electrode piercesneural tissue for better electrical contact. U.S. Pat. No. 5,215,088 toNormann describes an array of spike electrodes for cortical stimulation.Each spike pierces cortical tissue for better electrical contact.

The art of implanting an intraocular prosthetic device to electricallystimulate the retina was advanced with the introduction of retinal tacksin retinal surgery. De Juan, et al. at Duke University Eye Centerinserted retinal tacks into retinas in an effort to reattach retinasthat had detached from the underlying choroid, which is the source ofblood supply for the outer retina and thus the photoreceptors. See,e.g., E. de Juan, et al., 99 Am. J. Ophthalmol. 272 (1985). Theseretinal tacks have proved to be biocompatible and remain embedded in theretina, and choroid/sclera, effectively pinning the retina against thechoroid and the posterior aspects of the globe. Retinal tacks are oneway to attach a retinal electrode array to the retina. U.S. Pat. No.5,109,844 to de Juan describes a flat electrode array placed against theretina for visual stimulation. U.S. Pat. No. 5,935,155 to Humayundescribes a retinal prosthesis for use with the flat retinal arraydescribed in de Juan.

US Patent Application 2003/0109903 to Berrang describes a Low profilesubcutaneous enclosure, in particular and metal over ceramic hermeticpackage for implantation under the skin.

SUMMARY OF THE INVENTION

The present invention is a non-destructive method of inspecting a bond,particularly a braze bond, in a hermetic package. The invention involvesa unique hermetic package design adapted for ultrasonic inspection and amethod of inspecting the package. This package and non-destructiveinspection process are particularly useful in implantable neuralstimulators such as visual prostheses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a hermetic package adapted forinspection by acoustic energy and an acoustic transducer.

FIG. 2 is an image and graph showing reflected acoustic energy from thepreferred hermetic package and how that reflected acoustic energy showsdefects.

FIG. 3 is a perspective view of the implanted portion of the preferredretinal prosthesis.

FIG. 4 is a side view of the implanted portion of the preferred retinalprosthesis showing the strap fan tail in more detail.

FIG. 5 is a perspective view of a partially built package showing thesubstrate, chip and the package wall.

FIG. 6 is a perspective view of the hybrid stack placed on top of thechip.

FIG. 7 is a perspective view of the partially built package showing thehybrid stack placed inside.

FIG. 8 is a perspective view of the lid to be welded to the top of thepackage.

FIG. 9 is a view of the completed package attached to an electrodearray.

FIG. 10 is a cross-section of the package.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is of the best mode presently contemplated forcarrying out the invention. This description is not to be taken in alimiting sense, but is made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe determined with reference to the claims.

The present invention is an improved hermetic package for implantingelectronics within a body. Electronics are commonly implanted in thebody for neural stimulation and other purposes. The improved packageallows for miniaturization of the package which is particularly usefulin a retinal or other visual prosthesis for electrical stimulation ofthe retina.

Braze materials can have varying degrees of wetting of a ceramicmaterial. This can leave voids in braze joints. There is a need for aninspection method which can detect those voids. It has been surprisinglyand unexpectedly shown that the use ultrasonic inspection includingacoustic micro imaging (AMI) and scanning acoustic microscopy (SAM) isvery useful for 100% success in inspection of braze joints.

Ultrasonic inspection allows a 100 percent inspection of braze jointsbecause ultrasonic inspection is not destructive. No furtherverification of braze runs is required with this method. Therefore, ahigh increase of the reliability of the device is achieved.

The use of Acoustic Micro Imaging (AMI) can be employed as a criticalnondestructive inspection technique when inspecting hermetic packagesfor defects and structural information. AMI works by sending very highfrequency sounds (MHz range ultrasound) into the sample. An observationis made of how the sound interacts with the sample. The significantinteraction occurs when a gas or vacuum space is encountered. In thiscase, all of the ultrasound is reflected from the interface. This makesAMI an extremely sensitive technique for finding defects in the materiallike delaminations, cracks and voids. Even air gap thicknesses below 250Angstroms are highly detectable using AMI. This makes AMI more sensitivethan any other technique for detecting air space type defects.

AMI is also sensitive to general material changes. Every material can becharacterized by a property called acoustic impedance. When a soundpasses from one material to another (such as at an interface) some orall of the energy is reflected at the boundary. The amount of ultrasoundreflected is determined by the difference in the acoustic impedances.The more different the materials are the more sound is reflected. Thisallows for characterizing material change at a boundary.

AMI makes finer analysis of bond quality changes possible based onsubtle reflection variations. In most cases, however, delaminations andvoids are the most critical since they have an immediate effect on bondquality.

AMI is particularly useful for optically opaque samples because unlikelight, the sound waves penetrate the materials. Metals and ceramics tendto be very good at propagating the sound, which allows the use of veryhigh frequencies for high detail imaging. Polymers tend to be moreattenuating to the ultrasound and require the use of lower frequency forbetter penetration.

It should be noted that human implantable devices require a high degreeof reliability. Braze cracks as small as a few angstroms, will allowsaline to enter the device over time and cause it to fail. Failure of animplanted device will result in expensive and possibly dangerous surgeryto replace or remove the implant. It is, therefore, critical to achievea zero failure rate in the hermeticity of an implantable device.

FIG. 1 shows the preferred hermetic package 14 as it is inspected. Thepackage includes a ceramic substrate 60 brazed to a metal ring 62 by abraze joint 61. After brazing electronics, 67, 68, and 70 are attachedto the ceramic substrate 60 and a mettle lid 84 is laser welded to themetal right 62 at weld joint 63. The braze joint 61 can be inspected bypassing the ultrasound transducer 5 over the ceramic substrate 60 abovethe braze joint 61. It is important that the braze joint 61 is paralleland proximate to the surface of the ceramic substrate 60 where theultrasonic transducer 5 passes over the device. Preferably, thethickness of the ceramic substrate 60 is less than 500 μm to allow forinspection. Since, ultrasonic inspection is based on reflected energythe thickness under the braze joint 61 is unimportant. It should benoted that ultrasonic inspection can be done after brazing before thepackage is completed, on the complete package, or both. Early inspectionavoids the cost of completing a defective package and late inspectionidentifies potential damage occurring late in the process.

FIG. 2 shows an AMI image of the bond in the preferred package. Thewhite circle shows the surface of a ceramic substrate. The edge of thecircle shows the image of the bond. Where it appears solid black (1) themeasurement of a good bond is shown. On the right side the spectra ofthe measurements are shown. The top spectrum [1] corresponds to the goodbond (1). This can be recognized by the low amplitudes. The secondspectrum [2] shows the measurement of a place with insufficient bond(2). This place (2) can be recognized in the AMI as being spattered withwhite spots and the second spectrum [2] shows high amplitude comparedwith the first spectrum. The third spectrum [3] shows the measurement ofthe ceramic surface (3). Since there is no bond high amplitudes areproduced in the spectrum.

FIGS. 3 to 10 show the preferred application of the inventive hermeticpackage, as a retinal prosthesis. While described in the context of aretinal prosthesis, it should be obvious to one of skill in the art thatthe present invention is applicable to any hermetic package where highreliability is critical. In particular, human implantable devices suchas visual prostheses, cochlear prostheses, deep brain stimulators,pacemakers, etc. are good applications for the present invention.

FIG. 3 is a perspective view of the implanted portion of the preferredretinal prosthesis. A flexible circuit 1 includes a flexible circuitelectrode array 10 which is mounted by a retinal tack (not shown) orsimilar means to the epiretinal surface. The flexible circuit electrodearray 10 is electrically coupled by a flexible circuit cable 12, whichpierces the sclera in the pars plana region, and is electrically coupledto an electronics package 14, external to the sclera. Further anelectrode array fan tail 15 is formed of molded silicone and attachesthe electrode array cable 12 to a molded body 18 to reduce possibledamage from any stresses applied during implantation.

The electronics package 14 is electrically coupled to a secondaryinductive coil 16. Preferably the secondary inductive coil 16 is madefrom wound wire. Alternatively, the secondary inductive coil 16 may bemade from a flexible circuit polymer sandwich with wire traces depositedbetween layers of flexible circuit polymer. The electronics package 14and secondary inductive coil 16 are held together by the molded body 18.The molded body 18 holds the electronics package 14 and secondaryinductive coil 16 end to end. This is beneficial as it reduces theheight the entire device rises above the sclera. The design of theelectronic package (described below) along with a molded body 18 whichholds the secondary inductive coil 16 and electronics package 14 in theend to end orientation minimizes the thickness or height above thesclera of the entire device. This is important to minimize anyobstruction of natural eye movement.

The molded body 18 may also include suture tabs 20. The molded body 18narrows to form a strap 22 which surrounds the sclera and holds themolded body 18, secondary inductive coil 16, and electronics package 14in place. The molded body 18, suture tabs 20 and strap 22 are preferablyan integrated unit made of silicone elastomer. Silicone elastomer can beformed in a pre-curved shape to match the curvature of a typical sclera.However, silicone remains flexible enough to accommodate implantationand to adapt to variations in the curvature of an individual sclera. Thesecondary inductive coil 16 and molded body 18 are preferably ovalshaped. A strap 22 can better support an oval shaped secondary inductivecoil 16.

Further it is advantageous to provide a sleeve or coating 50 thatpromotes healing of the sclerotomy. Polymers such as polyimide, whichmay be used to form the flexible circuit cable 12 and flexible circuitelectrode array 10, are generally very smooth and do not promote a goodbond between the flexible circuit cable 12 and scleral tissue. A sleeveor coating of polyester, collagen, silicone, Gore-tex or similarmaterial would bond with scleral tissue and promote healing. Inparticular, a porous material will allow scleral tissue to grow into thepores promoting a good bond.

It should be noted that the entire implant is attached to and supportedby the sclera. An eye moves constantly. The eye moves to scan a sceneand also has a jitter motion to improve acuity. Even though such motionis useless in the blind, it often continues long after a person has losttheir sight. By placing the device under the rectus muscles with theelectronics package in an area of fatty tissue between the rectusmuscles, eye motion does not cause any flexing which might fatigue, andeventually damage, the device.

FIG. 4 shows a side view of the implanted portion of the retinalprosthesis, in particular, emphasizing the strap fan tail 24. Whenimplanting the retinal prosthesis, it is necessary to pass the strap 22under the eye muscles to surround the sclera. The secondary inductivecoil 16 and molded body 18 must also follow the strap 22 under thelateral rectus muscle on the side of the sclera. The implanted portionof the retinal prosthesis is very delicate. It is easy to tear themolded body 18 or break wires in the secondary inductive coil 16 orelectrode array cable 12. In order to allow the molded body 18 to slidesmoothly under the lateral rectus muscle, the molded body 18 is shapedin the form of a strap fan tail 24 on the end opposite the electronicspackage 14.

Referring to FIG. 5, the hermetic electronics package 14 is composed ofa ceramic substrate 60 brazed to a metal case wall 62 which is enclosedby a laser welded metal lid 84. The metal of the wall 62 and metal lid84 may be any biocompatible metal such as, but not limited to Titanium,niobium, platinum, iridium, palladium or alloys of such metals. Theceramic substrate is preferably alumina but may include other ceramicssuch as Yttrium Stabilized zirconia (YSZ). The ceramic substrate 60includes vias 65 made from biocompatible metal and a ceramic binderusing thick-film techniques. The biocompatible metal and ceramic binderis preferably platinum flakes in a ceramic paste or frit which is theceramic used to make the substrate. After the vias 65 have been filled,the substrate 60 is fired and lapped to thickness. The firing processcauses the ceramic to vitrify biding the ceramic of the substrate withthe ceramic of the paste forming a hermetic bond. Thin-filmmetallization 66 is applied to both the inside and outside surfaces ofthe ceramic substrate 60 and an ASIC (Application Specific IntegratedCircuit) integrated circuit chip 64 is flip-chip bonded to the thin filmmetallization on the inside of the ceramic substrate 60.

The inside thin film metallization 66 includes a gold layer to allowelectrical connection using wire bonding. The inside film metallizationincludes preferably two to three layers with a preferred gold top layer.The next layer to the ceramic is a titanium or tantalum or alloy thereofor other adhesion promoting metal or alloy. The next layer is preferablypalladium or platinum layer or an alloy thereof. The preferredmetallization includes a titanium, palladium and gold layer, but othercombinations that yield acceptable adhesion and resistance to hightemperature diffusion are possible. Gold is a preferred top layerbecause it is corrosion resistant and can be cold bonded with gold wire.

The outside thin film metallization includes a titanium adhesion layerand a platinum layer for connection to platinum electrode array traces,but other combinations that yield acceptable adhesion and resistance tohigh temperature diffusion are possible. for example platinum can besubstituted with palladium or palladium/platinum alloy. If gold-goldwire bonding is desired a gold top layer is applied.

The package wall 62 is brazed to the ceramic substrate 60 in a vacuumfurnace using a braze material in the braze joint. Preferably, the brazematerial is a nickel titanium or similar alloy. The braze temperature isapproximately 1000° Celsius. Therefore the vias 65 and thin filmmetallization 66 must be selected to withstand this temperature. Also,the electronics must be installed after brazing. The chip 64 isinstalled inside the package using thermocompression flip-chiptechnology. The chip is underfilled with epoxy to avoid connectionfailures due to stresses caused by thermal mismatch or vibration.

Referring to FIGS. 6 and 7, off-chip electrical components 70, which mayinclude capacitors, diodes, resistors or inductors (passives), areinstalled on a stack substrate 72 attached to the back of the chip 64,and connections between the stack substrate 72 and ceramic substrate 60are made using gold wire bonds 82. The stack substrate 72 is attached tothe chip 64 with non-conductive epoxy, and the passives 70 are attachedto the stack substrate 72 with conductive epoxy.

Referring to FIG. 8, the electronics package 14 is enclosed by a metallid 84 that, after a vacuum bake-out to remove volatiles and moisture,is attached using laser welding. A getter (moisture absorbent material)may be added after vacuum bake-out and before laser welding of the metallid 84. The metal lid 84 further has a metal lip 86 to protectcomponents from the welding process and further insure a good hermeticseal. The entire package is hermetically encased. Hermeticity of thevias 65, braze 61, and the entire package is verified throughout themanufacturing process. The cylindrical package was designed to have alow profile to minimize its impact on the eye when implanted.

The implant secondary inductive coil 16, which provides a means ofestablishing the inductive link between the external video processor(not shown) and the implanted device, preferably consists of gold wire.The wire is insulated with a layer of silicone. The secondary inductivecoil 16 is oval shaped. The conductive wires are wound in definedpitches and curvature shape to satisfy both the electrical functionalrequirements and the surgical constraints. The secondary inductive coil16, together with the tuning capacitors in the chip 64, forms a parallelresonant tank that is tuned at the carrier frequency to receive bothpower and data.

Referring to FIG. 9, the flexible circuit 1, includes platinumconductors 94 insulated from each other and the external environment bya biocompatible dielectric polymer 96, preferably polyimide. One end ofthe array contains exposed electrode sites that are placed in closeproximity to the retinal surface 10. The other end contains bond pads 92that permit electrical connection to the electronics package 14. Theelectronic package 14 is attached to the flexible circuit 1 using aflip-chip bumping process, and epoxy underfilled. In the flip-chipbumping process, bumps containing conductive adhesive placed on bondpads 92 and bumps containing conductive adhesive placed on theelectronic package 14 are aligned and cured to build a conductiveconnection between the bond pads 92 and the electronic package 14. Leads76 for the secondary inductive coil 16 are attached to gold pads 78 onthe ceramic substrate 60 using thermal compression or thermosonicbonding, and are then covered in epoxy. The junction of the secondaryinductive coil 16, array 1, and electronic package 14 are encapsulatedwith a silicone overmold 90 that connects them together mechanically.When assembled, the hermetic electronics package 14 sits about 2 mm awayfrom the end of the secondary inductive coil.

Since the implant device is implanted just under the conjunctiva it ispossible to irritate or even erode through the conjunctiva. Erodingthrough the conjunctiva leaves the body open to infection. We can doseveral things to lessen the likelihood of conjunctiva irritation orerosion. First, it is important to keep the over all thickness of theimplant to a minimum. Even though it is advantageous to mount both theelectronics package 14 and the secondary inductive coil 16 on thelateral side of the sclera, the electronics package 14 is mounted higherthan, but not covering, the secondary inductive coil 16. In other wordsthe thickness of the secondary inductive coil 16 and electronics packageshould not be cumulative.

It is also advantageous to place protective material between the implantdevice and the conjunctiva. This is particularly important at thescleratomy, where the thin film electrode array cable 12 penetrates thesclera. The thin film electrode array cable 12 must penetrate the sclerathrough the pars plana, not the retina. The scleratomy is, therefore,the point where the device comes closest to the conjunctiva. Theprotective material can be provided as a flap attached to the implantdevice or a separate piece placed by the surgeon at the time ofimplantation. Further material over the scleratomy will promote healingand sealing of the scleratomy. Suitable materials include Dacron, Teflon(polytetraflouroethylene or PTFE), Goretex (ePTFE) Tutoplast (sterilizedsclera), Mersilene (Polyester) or silicone.

Referring to FIG. 10, the package 14 contains a ceramic substrate 60,with metallized vias 65 and thin-film metallization 66. The package 14contains a metal case wall 62 which is connected to the ceramicsubstrate 60 by braze joint 61. On the ceramic substrate 60 an underfill69 is applied. On the underfill 69 an integrated circuit chip 64 ispositioned. On the integrated circuit chip 64 a ceramic hybrid substrate68 is positioned. On the ceramic hybrid substrate 68 passives 70 areplaced. Wirebonds 67 are leading from the ceramic substrate 60 to theceramic hybrid substrate 68. A metal lid 84 is connected to the metalcase wall 62 by laser welded joint 63 whereby the package 14 is sealed.

Accordingly, what has been shown is an improved method making a hermeticpackage for implantation in a body. While the invention has beendescribed by means of specific embodiments and applications thereof, itis understood that numerous modifications and variations could be madethereto by those skilled in the art without departing from the spiritand scope of the invention. It is therefore to be understood that withinthe scope of the claims, the invention may be practiced otherwise thanas specifically described herein.

What we claim is:
 1. A hermetic package comprising: a top having an edgesurface; a bottom having an outside surface and an inside surface; abond attaching said edge surface to said inside surface, wherein saidtop, bottom and bond form a rigid, biocompatible, hermetic packagesuitable for implantation within a human body; and wherein said bond isparallel to and sufficiently proximate to the outside surface to reflectultrasound energy and define said bond in an ultrasonic image.
 2. Thehermetic package according to claim 1, wherein said bond is less than500 μm from the outside surface.
 3. The hermetic package according toclaim 1, wherein said bond is selected from the group consisting of abraze bond and a solder bond.
 4. The hermetic package according to claim1, wherein said top and said bottom are selected from the groupconsisting of a metal and a ceramic.
 5. The hermetic package accordingto claim 1, wherein said hermetic package is biocompatible.
 6. Thehermetic package according to claim 5, wherein said hermetic package issuitable for implantation within a human body as a neural stimulator. 7.The hermetic package according to claim 6, wherein said hermetic packageis suitable for implantation within a human body as a visual prosthesis.